1. The Field of the Invention
This invention relates to photographic products. More precisely, the invention disclosed herein relates to photographic products especially useful in providing image patterns by way of diffusion transfer photographic processes.
2. Description of the Prior Art
Diffusion transfer photographic processes and photographic products adapted for such processes are well known to the art. Essentially, such products and processes involve a photosensitive system which is exposed to activating radiation. After exposure, the resultant image can be developed to provide a diffusion transfer image which can be transferred to an image receiving sheet. Details relating to some of the better known diffusion transfer photographic products and processes can be found in U.S. Pat. Nos. 2,983,606, 3,415,644 3,415,645; 3,415,646; 3,473,925; 3,573,042; 3,573,043; 3,573,044; 3,576,625; 3,576,626; 3,578,540; 3,579,333; 3,473,925; 3,594,164; and 3,594,165 as well as in commonly assigned U.S. Pat. Nos. 3,573,043; 3,573,044 and 3,672,890. All of the above Patents and Applications are expressly incorporated herein in their entirety by reference.
Photosensitive systems employed in the products and processes of the type described in the above-mentioned Patents and Applications comprise at least one selectively sensitized silver halide layer integrated with a dye image-providing material. Moreoften, however, such diffusion transfer photographic products and processes include a photosensitive system which can provide a multicolor diffusion transfer image and photosensitive systems of this type essentially include a blue, a green and a red sensitive silver halide layer each integrated respectively with a yellow, a magenta and a cyan dye image-providing material.
Suitable dye image-providing employed in diffusion transfer photosensitive systems are those which are either (1) initially soluble or diffusible in the processing composition but are selectively rendered non-diffusible as a function of development; or (2) initially soluble or non-diffusible in the processing composition but are selectively rendered diffusible as a function of development. Accordingly, suitable dye image-providing materials may be complete dyes or dye intermediates, e.g., color couplers and especially preferred materials are those known to the art as "dyed developers", e.g., a dye which is also a silver halide developing agent.
Examples of and details relating to initially soluble or diffusible materials and their application in color diffusion transfer, can be found in U.S. Pat. Nos. 2,647,049; 2,661,293; 2,698,244; 2,698,798; 2,802,735; 2,774,668 and 2,983,606. Examples of and details relating to diffusion transfer systems employing initially non-diffusible materials can be found in U.S. Pat. Nos. 3,443,939; 3,443,940; 3,227,550; 3,227,551; 3,227,552; 3, 227,554; 3,243,294; and 3,445,228.
Diffusion transfer photographic products of the type disclosed and claimed in U.S. Pat. Nos. 3,415,644, and 3,647,437 are distinctive in that they are adapted for use under circumstances where at least a portion of the processing of the exposed photosensitive system is conducted under conditions which would ordinarily result in further exposure or fogging of the photosensitive system. Essentially, products of the type disclosed in the above Patents comprise a photosensitive component and an image-receiving component maintained in fixed relationship prior to exposure as well as after exposure and processing. In such products, which are sometimes called "integral negative-positive photographic products", the final image is viewed through a transparent layer or support against a reflecting background.
In the particularly preferred products, exposure is made through the transparent member while a light-reflecting material which can provide a reflecting background is included in the processing composition to be distributed between the exposed photosensitive element. The preferred light-reflecting material for inclusion in the processing composition is titanium dioxide which in addition to providing a suitable reflective background also performs an opacifying function by protecting the exposed photosensitive system from fogging or further exposure if the exposed product is subjected to activating radiation after photoexposure. This protection is provided during that period extending from immediately after processing is begun and continues until at least the time that development of the photoexposure is complete and/or until that time that any subsequently exposed portions of the photosensitive system cannot be developed by the processing composition involved in development of the photoexposed material.
Especially preferred integral negative-positive photographic products are those disclosed in U.S. Pat. No. 3,647,437. Such products employ a light-absorbing material or reagent--preferably a dye--to protect the exposed photosensitive system for activating radiation after photoexposure. Essentially, the light-absorbing reagent is so positioned and/or constituted so as not to intefere with photoexposure but to absorb activating radiation during development until development of the photoexposed image is complete and/or fogging cannot occur. Additionally, the light absorbing reagent is so positioned and/or constituted that it does not obstruct viewing of the diffusion transfer image at least after the image is formed in the image-receiving sheet and, in some instances, the material does not obstruct viewing of the image during a portion of the time involved in the formation of the image in the receiving sheet.
Particularly preferred light-absorbing materials of U.S. Pat. No. 3,647,437 are indicator dyes which are highly colored at the pH of the processing composition but are "cleared", e.g., rendered substantially colorless or non light absorbing at a lower pH. Especially preferred photographic products of U.S. Pat. No. 3,647,437 are those where the light-absorbing reagent is included in the processing composition together with the light-reflecting material so that both reagent and reflecting material are distributed between the photosensitive element and the image-receiving element after photoexposure.
A known diffusion transfer photographic product particularly suitable for providing monochrome or multicolor diffusion transfer image patterns of or comprising green, cyan or blue colors is one employing phthalocyanine dye developers of the type described in U.S. Pat. No. 3,482,972 issued to Elbert M. Idelson on Dec. 9, 1969. Dye developers of the type disclosed there are those conforming to the following formula: ##STR1## where that of the 16 R substituents present on the phthalocyanine ring at least one and no more than four are as R.sup.1 groups, there being no more than two R.sup.1 groups on any one benzene ring, the remaining R substituents being R.sup.2 groups, and R.sup.1 comprises a group (--A).sub.n --E; A is a divalent organic linking radical; n is a number of from 0 to 1; E is an aryl group selected from the group consisting of benzene and naphthalene radicals so substituted by at least two groups selected from the group consisting of hydroxyl and amino groups which are situated ortho or para to each other as to be capable of developing an exposed silver halide photographic emulsion; M is a metal selected from the group consisting of cobalt, nickel, copper, chromium, magnesium and zinc; and each R.sup.2 comprises the same or a different moiety selected from the group consisting of monovalent organic and monovalent inorganic radicals, neither of which contain a silver halide developing radical, and hydrogen. Most preferred are those cyan dyes within the above formula wherein the metal moiety is copper and these dye developers may be referred to simply as copper phthalocyanine dye developers.
U.S. Pat. No. 3,770,439 issued to Lloyd D. Taylor on Nov. 6, 1973 relates to improved photographic products particularly those employing phthalocyanine dye developers of the type described above. As disclosed in U.S. Pat. No. 3,770,439, improved diffusion transfer of such phthalocyanine dyes is obtained by the use of an image-receiving sheet which comprises a polymeric material providing quaternary nitrogen groups usually in combination with other polymeric materials. Specific polymeric materials providing quaternary nitrogen groups disclosed in U.S. Pat. No. 3,770,439 include polymers comprising the following entity: ##STR2## where each R.sup.1 can be the same or different substituent chosen from the group consisting of hydrogen, hydroxyl, alkyl, alkoxy or alkanol and preferably lower alkyl, alkoxy or alkanol, e.g., wherein the hydrocarbon moiety contains 1-6 carbon atoms and X.sup.- is an anion radical.
Although improved diffusion transfer rates for phthalocyanine dye developers are obtained by the use of image receiving sheets comprising a polymeric material providing quaternary nitrogen groups, a deficiency has been noted in those photographic products comprising such receiving sheets in combination with the light-absorbing reagents of the type disclosed in U.S. Pat. No. 3,647,437. As discussed before, the function of such reagents is to provide protection for the photoexposed material from fogging and, to be "cleared", e.g., rendered substantially colorless after such protection is no longer required so that viewing of the diffusion transfer image is not obstructed. It should be understood that the time required for the reagent to provide the protective function is not necessarily equivalent to the time required for complete formation of the image in the image-receiving sheet. Actually, an especially desirable performance characteristic for such reagents is that they "clear" as soon as possible after the protective function is no longer required and in many instances, such protection need not be provided until the image is completely formed in the image-receiving sheet. Instead, "clearing" can oftentimes occur prior to complete formation of the image thereby permitting viewing of the image against a reflective background during formation thereof.
The ability of a light-absorbing reagent to clear as quickly as possible after performing its protective function is especially desirable in photographic products providing accelerated diffusion rates for dyes comprising the diffusion transfer image pattern. However, when light-absorbing reagents of the type disclosed in U. S. Pat. No. 3,647,437 are included in products employing image receiving layers comprising a polymeric material providing quaternary nitrogen groups, the rate of clearing of such reagents has been found to be undesirably slow. In other words, such photographic products provide accelerated image formation in the image-receiving sheet but the rate of clearing of the light-absorbing reagent is undesirable especially in view of the accelerated image formation. The precise cause of this slow clearing of the light-absorbing reagent is not known. However, since clearing is primarily dependent on pH, there may be some chemical or physical interaction between the reagent and the polymeric material providing the quaternary nitrogen groups which interferes with or affects the response of the reagent to pH to quickly change from a light-absorbing to a substantially colorless state.
The present invention is addressed to the above described photographic products and provides photographic products and processes wherein the rate of clearing of light-absorbing reagents is markedly improved despite the presence in image-receiving sheets of such products of polymeric materials providing quaternary nitrogen groups.